A fillet of salmon is not half a salmon..half of a salmon is huge. One fillet is usually about 140g and has about 28g of protein if it's good quality also about 19g of fat.

A fillet of salmon is actually half the salmon cut along the backbone. Basically any portion of fish that does not have any bones could be called a fillet. As opposed to a salmon or tuna steak that has a part of the backbone in it.